Magnet wire insulation consists of enamel baked on bare copper wire. The wire is enameled by dipping the wire in liquid enamel, baking, redipping and rebaking repeatedly until the desired electrical insulation and mechanical properties are achieved.
A standard practice in the prior art is to select the desired wire gauge to be enameled and have a large quantity of the desired gauge wire predrawn and placed on hand and available for fabrication. Recently, it has become the practice in the assignee's magnet wire fabrication plants to provide "in-line" drawing machines for drawing wire simultaneously with the fabrication process. Baskets of heavy gauge wire feed drawing machines which draw wire down to the desired gauge. The wire is then passed through an annealer and then dipped and baked prior to spooling. All of these processes take place in a single fabrication line.
A large number of "in-line" fabrication lines have been established at assignee's fabrication plant. Because of the criticality of the enameling process, involving closely controlled temperatures and airflows for curing the enamel, an external supply of electrical power for pulling the wire through the enameling process cannot be depended upon. Therefore, an in-house generator is utilized to provide closely regulated electrical power for the pulling of wire through the dipping and baking process.
On the other hand, electrical power for the drawing machine variable speed motors cannot be economically supplied in-house because of the very large power demand.
Because of the "in-line" character of the production process it will be seen that if there is a "dip" in the voltage supplied by the utility for driving the wire drawing machines, there will be a slowdown in those motors which will in turn cause wire to be supplied to the enameling end of the fabrication process line in a not large enough quantity to remain sufficiently supplied. This is due to the steady character of the voltage supplied from the "in-house" generator which is not subject to the utility line dips in voltage.
Thus, unless there is a wire accumulator provided between the wire drawing end of the fabrication line and the enameling end of the line there may be a wire breakage during a utility line voltage dip.
In evolving an apparatus and method for controlling the speed of the wire drawing motors vis-a-vis the capstan motor (which pulls the wires in unison through the enameling end of the line), Applicant's assignee has, over the past few years, established a control principle based upon a "mixing" technique in which the speed of the pulling capstan at the enameling end is monitored and provided to the drawing end in order to use that signal as an indication of how fast the drawing machines should be running. However, because of component differences between variable speed motor drive controllers and motors, even if the same speed command signal is used for controlling each motor, there will be slight differences in the resulting speed of the various motors in a multiple wire drawing machine Therefore, the magnitude of the speed signal provided to each variable speed motor drive must be modified slightly to account for these differences. This may be handled by sensing the amount of wire accumulated in each of the channels of the accumulator. If the accumulator is accumulating a little bit too much wire it is a good indication that the speed of the drawing machine is a little bit too fast and an appropriately scaled signal can be fed back to modify the speed command signal so as to slow it down slightly. The same goes for the situation where the accumulator is accumulating not enough wire to withstand a utility voltage dip. In that case, the signal from the accumulator is used to slightly increase the speed of the drawing machine motor to provide a little bit more wire accumulation.
In this way, the proper amount of accumulated wire for each of the channels in the accumulator can be assured. This principle has been in use in assignee's plant for more than one year for producing wire in commercial quantities.
However, the circuitry for mixing the capstan speed signal and the accumulator signal is somewhat complex and needs to be adjusted for each of the lines individually by a technician using manual adjustments. This can be somewhat confusing for the technicians, many of whom are not schooled or equipped to make delicate electronic adjustments without error. Furthermore, each time the wire gauge is changed there is a necessity to provide more or less accumulation of wire because of the different speeds used to fabricate different gauges. This also requires manual adjustments, different from the previously mentioned adjustments, which gives rise to further confusion on the part of the technicians.